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One small step for bio-bots

Use it or lose it: steerable miniature worm-like robots built with live muscle cells get stronger with a little personal training. Cathal O'Connell reports.

Meet a new class of modular muscle-powered walking bio-bots that respond to light. – Ritu Raman, University of Illinois

Cyborgs – living creatures augmented with robotic machinery – have been a freaky staple of science fiction for decades. Now take that idea and turn it inside out. What about a robot powered by living muscle?

What’s more, they found they could strengthen the bio-bots by putting them through an exercise regime. The researchers see it as a big step towards miniature bots as autonomous sensors or vehicles to deliver drugs.

Though real muscle is not as strong, for its weight, as the strongest artificial muscles, it’s still a superbly engineered actuator.

With a simple contracting mechanism and no articulating parts, muscle can be adapted to almost any shape. And if put to work in a biological medium, muscle needs no onboard power source – often the bane of miniature bot-makers.

In 2014, a group led by Rashid Bashir at the University of Illinois showed off an earlier version of their bio-bot, or “muscle powered biological machines”. At that stage the team could trigger bio-bots to drag themselves slowly across a substrate, but without a controllable steering mechanism.

'Inching' is the perfect verb – their top speed is a bit less than two centimetres a minute.

Now, using the new technology of optogenetics, Bashir’s group has genetically engineered the muscle cells to respond to blue light. A flash of light causes the muscle cells to contract, and the bug-sized frankenbot crawls forward like an inchworm.

And “inching” is the perfect verb – their top speed is a bit less than two centimetres a minute.

The major new advance is how they can use light as a steering mechanism. Shining the light beam at either side of the bot activates different muscle cells, which pulls the bot in either direction.

To make their bio-bot, the researchers grew rings of genetically engineered muscle tissue from a mouse. The researchers then looped the rings of muscle around a 3-D printed crawler.

After subjecting the bio-bots to some personal training – a five-minute exercise regime per day – the bio-bots got stronger, with a 550% increase in the forces generated after about two weeks. This meant the bio-bots could adapt to particular tasks, say the researchers.

Bashir sees the design’s flexibility as the key towards making more complex biological machines: "With the rings, we can connect any two joints or hinges on the 3-D-printed skeleton. We can have multiple legs and multiple rings.”

One application he has in mind for the bio-bots is as autonomous sensors – able to move towards a particular toxin in the body, then release agents to neutralise it.

In the nearer term, the muscles could be used as pumps or valves to push liquids around fluidic devices or as little flippers for swimmer-bots.

Seems like the gap between “life” and “machine” is slowly closing (at about two centimetres a minute).